Polymer electrolyte composite film, method for production thereof and use thereof

ABSTRACT

A polymer electrolyte composite film which comprises a porous base material and, provided in fine pores thereof, a polymer electrolyte comprising a hydrophilic moiety and a hydrophobic moiety, the hydrophilic and hydrophobic moieties of said polymer electrolyte satisfy the following formula (1): a+b≦d (1) [wherein, a represents the size of a hydrophobic domain (nm), b represents the size of a hydrophilic domain (nm), and d represents the average pore diameter (nm) of fine pores of the porous base material].

TECHNICAL FIELD

The present invention relates to a polymer electrolyte compositemembrane having a composite layer comprising a porous base materialhaving fine pores which is filled with a polymer electrolyte comprisinga hydrophobic moiety and a hydrophilic moiety, its manufacturing method,and its use.

BACKGROUND ART

Recently, fuel cells (solid polymer electrolyte type fuel cell) using aproton conductive membrane as an electrolyte are actively developed.Solid polymer electrolyte type fuel cells have features of operating ata low temperature, having high output per unit area and of capable ofbeing downsizing. Due to these features, solid polymer electrolyte typefuel cells have a promising use for on-vehicle power supply, etc. due tothe features, and some polymer electrolyte membranes as a basic materialthereof are proposed.

For example, JP-A-6-29302 proposed a polymer electrolyte compositemembrane in which a polymer electrolyte is provided in a porous basematerial. The composite layer has more improved mechanical strength incomparison with a membrane comprising a polymer electrolyte, however,its ion conductivity is not sufficient and satisfactory power generatingperformance is not obtained.

An objective of the present invention is to provide a polymerelectrolyte composite membrane that exhibits high power generatingperformance, its manufacturing method and its use.

DISCLOSURE OF INVENTION

Inventors of the present invention made vigorous investigation onpolymer electrolytes so as to find a polymer electrolyte compositemembrane that exhibits high power generating performance, as a result,the inventors found out that when a porous base material is filled witha polymer electrolyte having a phase-separated structure of ahydrophobic moiety and a hydrophilic moiety in a solid state, and thesum of the size of hydrophobic domain and that of hydrophilic domain inthe phase-separated structure equal to or less than a size of averagepore diameter of fine pores of a porous base material, an electrolytecomposite membrane thus obtained exhibits high power generatingperformance, furthermore, the inventors carried out various examinationsto complete the invention.

That is, the invention provides a polymer electrolyte composite membranecomprising a porous base material having fine pores which is a polymerelectrolyte comprising a hydrophobic moiety and a hydrophilic moiety,and the polymer electrolyte forms a phase-separate structure of eachphase of a hydrophobic moiety and a hydrophilic moiety in a solid state,and the each phase satisfy the following formula (1)a+b≦d  (1)(In the formula, a represents the size (nanometer) of a hydrophobicdomain, b represents the size (nanometer) of a hydrophilic domain in aphase-separated structure, and d represents the average pore diameter(nanometer) of fine pores of a porous base material).

Further, the invention provides a method for manufacturing the polymerelectrolyte composite membrane.

Further, the invention provides a fuel cell using the polymerelectrolyte composite membrane.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a first diagram of how to obtaining the sum of the size ofhydrophobic domain a and that of hydrophilic domain b.

FIG. 2 is a second diagram of how to obtaining the sum of the size ofhydrophobic domain a and that of hydrophilic domain b.

REFERABLE EMBODIMENT FOR CARRYING OUT THE INVENTION

Hereinafter, the details of the present invention will be explained.

A polymer electrolyte composite membrane according to the inventionforms a phase-separate structure of a hydrophobic moiety and ahydrophilic moiety in a solid state and a relationship among the size ofa (nanometer, nm) of a hydrophobic domain, the size of b (nm) of ahydrophilic domain and d (nm) of the average pore diameter of a finepore of a porous base material satisfies the formula (1).

Here, the size of a (nm) of a hydrophobic domain, and the size of b (nm)of a hydrophilic domain can be measured, for example, by transmissionelectron microscope, small-angle X ray diffraction, and the like.

It is preferable to use a transmission electron microscope among them. Amethod for measuring a and b include, for example, a step of dyeing ahydrophobic phase and a hydrophilic phase in different colors by dyeingan ultra-thin piece of film of polymer electrolyte having a hydrophobicmoiety and a hydrophilic moiety, which is cut in a film thicknessdirection, in an ordinary manner; a step of measuring an value ofdiameter of at least ten maximum circles included in respective phases;and a step of calculating an average value of the respective diametersof maximum circle of the respective phases. An average value of therespective diameters thus obtained is set to be a size a (nm) of ahydrophobic domain or a size b (nm) of a hydrophilic moiety. Further,a+b of the sum of the size of a hydrophobic domain and that of ahydrophilic domain may be calculated by using the obtained values orwhen a polymer electrolyte forms a continuous phase-separated structureof a hydrophobic moiety and hydrophilic moiety, a value of the diameterof maximum circle included both in a hydrophobic phase and a hydrophilicphase, which are dyed in different colors, is measured at least tencircles, and an average of the measured values may be used as theaverage value.

In a case of lamellar structure having a continuous phase-separatedstructure of a hydrophobic moiety and hydrophilic moiety (FIG. 1), acircle included in the each phase is set to be a₁ or b₁. Further, amaximum circle included in both of the phases is set to be A₁. Further,in a case of lamellar structure having an uneven thickness (FIG. 2), acircle included in the respective phases is set to be a₂ or b₂. Further,a maximum circle included in both of the phases is set to be A₂. Morethan ten circles thus determined are selected from the different partsand an average of the diameters may be set to a size of a of ahydrophobic domain or a size of b of a hydrophilic domain.Alternatively, a value of the diameter of maximum circle may be set tobe the sum of value a+b (nm).

A polymer electrolyte to be used in the invention should satisfy theformula (1), that is, a relationship between a value of a+b, obtained byany of the above methods, and an average value of d (nanometer) of porediameter of fine pores of a porous base material should satisfy theformula (1).

In making a film of a polymer electrolyte, it is preferable to use afilm manufactured by using the same solvent and under the same dryingcondition as that in manufacturing a polymer electrolyte compositemembrane that will be described below.

It is more preferable that a relationship between a+b and d satisfiesa+b≦d/2.

A value of (a+b) of the sum of a and b is usually equal to or more thanone nanometer, preferably equal to or more than three nanometers, andmore preferably equal to or more than ten nanometers. Further, it isusually equal to or less than 200 nanometers, preferably equal to orless than 100 nanometers, and more preferably equal to or less than 80nanometers.

A hydrophilic moiety of polymer electrolyte have a repeating unit havinghydrophilic property. An example of the repeating unit havinghydrophilic property includes a repeating unit having an ion-exchangegroup, and the ion-exchange group includes a cation-exchange group suchas —SO₃H, —COOH, —PO(OH)₂, —POH(OH), or —Ph(OH) (Ph represents a phenylgroup) and an anion-exchange group such as —NH₂, —NHR, —NRR′, —NRR′R″⁺,—NH₃ ⁺ (R represents an alkyl group, a cycloalkyl group, an aryl group,etc.). A part or whole of these groups may form salt with counter ions.Further, a repeating unit including a group such as —SO₂NHSO₂— in a mainchain of polymer may be included in a repeating unit having hydrophilicproperty.

A hydrophobic moiety of polymer electrolyte have a repeating unit havinghydrophobic property. The repeating unit having hydrophobic propertyincludes a repeating unit having none of the ion-exchange groups and agroup such as —SO₂NHSO₂—.

When both of the repeating unit having hydrophilic property and thathaving hydrophobic property present in a polymer, these repeating unitsare chemically different each other, due to interaction between therepeating units, usually, the polymer has a phase-separated structure ofa domain comprising a hydrophobic repeating unit and that comprising ahydrophilic repeating unit, that is, a domain comprising a hydrophobicmoiety and that comprising a hydrophilic moiety, in a nanometer scale.

In the invention, it is preferable that respective domains have acontinuous phase-separated structure, respectively, and it is morepreferable that they have a phase-separated structure in whichrespective phases are parallel to a film thickness direction (equivalentto FIG. 1).

An example of polymer electrolyte having the phase-separated structureincludes

-   (A) polymer electrolyte having any one of a sulfonic acid group and    a phosphonic acid group or both that is introduced in a main chain    of a copolymer of aliphatic hydrocarbon; (B) polymer electrolyte    having any one of a sulfonic acid group and a phosphonic acid group    or both that is introduced in a copolymer having aliphatic    hydrocarbon in a main chain whose a part or the whole of hydrogen    atoms are substituted with a fluorine atom; (C) polymer electrolyte    having any one of a sulfonic acid group and a phosphonic acid group    or both that is introduced in a polymer having a main chain    containing aromatic ring; (D) polymer electrolyte having any one of    a sulfonic acid group and a phosphonic acid group or both that is    introduced in a polymer having a main chain that substantially    includes none of carbon atoms; (E) polymer electrolyte having any    one of a sulfonic acid group and a phosphonic acid group or both    that is introduced in a copolymer comprising two or more of    repeating units selected from the group consisting of repeating    units of polymer which is polymer prior to introducing any one of    sulfonic acid group and phosphonic acid or both into polymer    electrolyte described in (A) to (D); and (F) polymer electrolyte    introduced an acidic compound, such as sulfuric acid or phosphoric    acid, by ion bond to a polymer including a nitrogen atom in a main    chain or a side chain.

The (A) polymer electrolyte includes, for example, polyvinyl sulfonicacid, polystyrene sulfonic acid, poly(α-methylstyrene) sulfonic acid.

The (B) polymer electrolyte includes a polymer, typified by Nafion(registered trademark manufactured by E.I. du Pont de Nemours Company,will be same hereinafter), having a side chain withperfluoroalkysulfonic acid and a main chain comprising perfluoroalkane;a sulfonic acid type polystyrene-graft-ethylene-tetrafluoroethylenecopolymer (ETFE, for example, disclosed by JP-A-9-102322) comprising amain chain formed by a copolymer of a fluorine carbide type vinylmonomer and a hydrogen carbide type vinyl monomer and a hydrogen carbidetype side chain having a sulfonic acid group; and a sulfonic acid typepoly(trifluorostyrene)-graft ETFE film (for example, disclosed by U.S.Pat. Nos. 4,012,303 and 4,605,685) comprising a solid polymerelectrolyte obtained by graft-polymerizing a film formed by a copolymerof a fluorine carbide type vinyl monomer and hydrogen carbide type vinylmonomer and a,β,β-trifluorostyrene, and introducing a sulfonic acidgroup thereto.

The (C) polymer electrolyte may include one having a main chaininterrupted by a hetero atom such as an oxygen atom, for example, apolymer electrolyte having a sulfonic acid introduced to a polymer suchas polyetheretherketone, polysulfone, polyethersulfone, poly(aryleneether), polyimide, poly((4-phenoxybenzoyl)-1,4-phenylene), polyphenylenesulfide, polyphenylquinoxsalene; sulfoarylated polybenzimidazole,sulfoalkylated polybenzimidazole, phosphoalkylated polybenzimidazole(for example, JP-A-H9-110982), phophosphonated poly(phenylene ether)(for example, J. Appl. Polym. Sci., 18, 1969 (1974)).

The (D) polymer electrolyte includes polyphosphazene to which a sulfonicacid group is introduced, polysiloxane having a phosphonic acid groupdescribed in Polymer Prep., 41, No. 1, 70 (2000), etc.

The (E) polymer electrolyte includes a polymer electrolyte having anyone of a sulfonic acid group and a phosphonic acid group or both that isintroduced in a random copolymer; a polymer electrolyte having any oneof a sulfonic acid group and a phosphonic acid group or both that isintroduced in an alternating copolymer; and a polymer electrolyte havingany one of a sulfonic acid group and a phosphonic acid group or boththat is introduced in a block copolymer. The polymer electrolyte havingany one of a sulfonic acid group and a phosphonic acid group or boththat is introduced in a random copolymer includes, for example,sulfonated polyethersulfone-dihydroxybiphenyl copolymer (for example,JP-A-11-116679).

The (F) polymer electrolyte includes, for example, polybenzimidazoleincluding phosphoric acid disclosed by JP-A-11-503262.

In a block copolymer included in the (E) polymer electrolyte, an exampleof block having any one of a sulfonic acid group and a phosphonic acidgroup or both is a block having any one of a sulfonic acid group and aphosphonic acid group or both disclosed by JP-A-2001-250567.

It is preferable that the polymer electrolyte according to the inventioncomprises a block copolymer or a graft copolymer, especially, it ispreferable that the polymer electrolyte comprises a polymer having amain chain with an aromatic ring such as the (C) polymer electrolyte,and it is more preferable that the polymer electrolyte comprises apolymer to which any one of a sulfonic acid group and a phosphonic acidgroup or both is introduced.

Weight molecular weight of polymer electrolyte used in the invention isusually approximately 1000 to approximately 1000000, and a value of ionexchange group equivalent weight is usually approximately 500 to 5000g/mol.

Additives such as a plasticizer, a stabilizer, a mold releasing materialused in ordinary polymers may be used within a range that does notcontradict to an objective of the invention.

According to the invention, the polymer electrolyte, which will bedescribed below, whose relationship between an average value of finepore diameter d (nanometer) of a porous base material satisfies theformula (1), is selected.

Here, it is preferable that a value obtained by bubble point method(ASTM F316-86) is used as an average value of fine pore diameter d(nanometer) of porous base material.

An average value of fine pore diameter d is usually one to approximately1,000,000 nanometers, is preferably approximately 30 to 10,000nanometers, and is more preferably approximately 50 to 1,000 nanometers.

A porous base material used in the invention has a polymer electrolytein its fine pores, and is used to further improve the strength,flexibility, and durability of the polymer electrolyte. Therefore, anyporous material that satisfies the intended use may be used, includesfor example, a porous film, woven fabric, nonwoven fabric and fibril,and may be used regardless of the shape or quality of material.

From the perspective of heat resistance, or stiffening effect ofphysical strength, an aliphatic based polymer, an aromatic basedpolymer, and a fluorine-containing polymer are preferable.

Here, an aliphatic based polymer includes polyethylene, polypropylene,polyvinyl alcohol, ethylene-vinyl alcohol copolymer, etc, but it is notlimited to them. Further, the term of polyethylene used here refers tothe general term of ethylene based polymer having a crystal structure ofpolyethylene, and includes, for example, a copolymer comprising ethyleneand other monomers, and specifically includes a copolymer referred to aslinear low density polyethylene (LLDPE) comprising a copolymer withethylene or α-olefin, or an ultrahigh molecular weight polyethylene,etc. Further, the term of polypropylene used here refers to the generalterm of propylene based polymers having a crystal structure ofpolypropylene, and includes a propylene based block copolymer, a randomcopolymer, etc. (these are copolymers comprising ethylene or 1-butene,etc), which are generally used.

An aromatic based polymer includes polyester, polyethyleneterephthalate, polycarbonate, polyimide, polysulfone, etc.

Further a fluorine-containing polymer includes a thermoplastic resinhaving at least one carbon-fluorine bond in a molecule. Usually, it ispreferably to use an aliphatic based polymer having a structure in whichall or most of hydrogen atoms are substituted by a fluorine atom.

The specific example includes polytrifluoroethylene,polytetrafluoroethylene, polychlorotrifluoroethylene,poly(tetrafluoroethylene-hexafluoropropylene),poly(tetrafluoroethylene-perfluoroalkylether), polyvinylidene-fluoride,etc, but it is not limited to them. Polytetrafluoroethylene andpoly(tetrafluoroethylene-hexafluoropropylene) are preferable among them,especially polytetrafluoroethylene is preferable. Further, it ispreferable that the fluororesin has an average molecular weight of100,000 or more, from the viewpoint of excellence of mechanicalstrength.

When the porous base material is used as a diaphragm for solid polymerelectrolyte type fuel cells, the film thicknesses is usually one toapproximately 100 micrometers, preferably approximately three toapproximately 30 micrometers, and further preferably approximately fiveto approximately 20 micrometers; the porosity is usually approximately20 to approximately 98%, preferably approximately 40 to approximately95%.

When a film thickness of porous base material is too thin, an effect ofincreasing the strength of polymer electrolyte composite membrane or astiffening effect such as imparting flexibility or durability isinsufficient and it is more likely to generate gas leakage (crossleakage). Alternatively, when a film thickness of porous base materialis too thick, an electric resistance becomes high, and a polymerelectrolyte composite membrane thus obtained becomes insufficient as adiaphragm. When the porosity is too small, the resistance as polymerelectrolyte composite membrane becomes large, and when the porosity istoo large, the strength of porous base material itself generally lowers,and the stiffening effect deteriorates.

Next, a method for manufacturing a polymer electrolyte compositemembrane will be explained.

In a method according to the invention, a polymer electrolyte and aporous base material that satisfy the formula (1) are used.

A method for compositing a polymer electrolyte and a porous basematerial to manufacture a polymer electrolyte composite membraneincludes a method of making a polymer electrolyte into solution,impregnating a porous base material with the solution, taking out theporous base material, and then drying solvent to manufacture a compositemembrane; a method of applying the solution on a porous base material,and drying solvent to manufacture a composite membrane, and a method ofcontacting the solution with a porous base material under reducedpressure, impregnating a fine pore of porous base material with thesolution by returning the pressure to a normal pressure, and dryingsolvent to manufacture a composite membrane, etc.

In a case of using solution of polymer electrolyte, there are noparticular limitations for solvents provided that they can be soluble,and relatively easily removed subsequently; an aprotic polar solventsuch as N,N-dimethyl formamide, N,N-dimethyl acetamide,N-methyl-2-pyrrolidone, or dimethyl sulfoxide; a chlorinated solventsuch as dichloromethane, chloroform, 1,2-dichloroethane, chlorobenzene,or dichlorobenzene; alcohol such as methanol, ethanol, or propanol; andalkylene glycol monoalkyl ether such as ethylene glycol monomethylether, ethylene glycol monoethyl ether, propylene glycol monomethylether, or propylene glycol monoethyl ether are preferably used. Any oneof the solvents can be used alone; however, two or more kinds ofsolvents can be mixed to use as need arises. From a viewpoint ofsolubility in polymer electrolyte, dimethyl acetamide, dimethylformamide, dimethyl sulfoxide and dichloromethane-methanol mixturesolvent are preferable.

A polymer electrolyte composite membrane according to the inventioncomprises a porous base material and, provided in fine pores thereof, apolymer electrolyte; or a polymer electrolyte composite membrane mayhave a polymer electrolyte layer provided on a surface of porous basematerial.

An electrolyte membrane or polymer electrolyte composite membrane may befurther layered on a polymer electrolyte composite membrane according tothe invention, a preferred embodiment includes a layer structure such as(polymer electrolyte composite membrane/electrolyte membrane),(electrolyte membrane/polymer electrolyte composite membrane/electrolytemembrane), and a layer structure such as (electrolyte membrane/polymerelectrolyte composite membrane/electrolyte membrane/polymer electrolytecomposite membrane/electrolyte membrane) formed by superposing the layerstructures. In the respective layer structures, any one of polymerelectrolyte composite membrane and electrolyte membrane or both may bedifferent each other or same.

Next, a fuel cell in which a polymer electrolyte composite membraneaccording to the invention is used will be explained.

A fuel cell comprises a plurality of unit cells laminated alternatelythrough a separator on which a gas passing unit is provided; each of theunit cells comprises an anode and a cathode provided on gas diffusionelectrodes provided opposing each other, and a film electrode assemblycomprising a polymer electrolyte film that selectively passes an ion,interposed between the both electrodes in contact with the electrodes.In the fuel cell, electricity is generated by using electrochemicalreaction generated by supplying fuel such as hydrogen, reformed gas,methanol to an anode and an oxidizing reagent such as oxygen to acathode; that is, fuel is oxidized electrocatalytically and an oxidizingagent is simultaneously reduced electrocatalytically, and chemicalreaction energy is directly transformed into electrical energy togenerate electricity.

Here, there are no particular limitations for catalytic agents providedthat they can activate oxidation-reduction with hydrogen or oxygen, anyknown catalytic agent may be used; however, it is preferable to use aparticle of platinum. A particle of platinum, supported by particulateor fibrous carbon such as activated charcoal or soft charcoal ispreferably used.

Any known conductive substance as current collecting body can be used;however, a porous carbon woven fabric and carbon paper are preferablebecause they effectively transport material gas to a catalyst.

Regarding a method for joining a particle of platinum or a particle ofplatinum supported by carbon to a porous carbon woven fabric or carbonpaper; and a method for joining that to a polymer electrolyte sheet, anyknow method such as a method described in J. Electrochem. Soc.:Electrochemical Science and Technology, 1988, 135(9), 2209, etc. can beused.

EXAMPLE

Hereinafter, examples will be explained; however, the present inventionis not limited thereto.

(Porous Base Material)

A polyethylene-made porous film described below manufactured accordingto JP-A-2002-309024 was used. A value obtained by bubble point methodASTM F316-86 was shown as an average value of fine pore diameter.

Polyethylene-based porous film A: average value of fine pore diameterd=60 nanometers

Polyethylene-based porous film B: average value of fine pore diameterd=40 nanometers

(Evaluation of Polymer Electrolyte Composite Membrane)

A platinum catalyst supported by fibrous carbon and porous carbon wovenfabric as current collector is jointed to both surfaces of polymerelectrolyte composite membrane. Wet oxygen gas was fed to one surface ofthe unit and wet hydrogen gas was fed to another surface to measure thepower generating characteristics.

Reference Example 1 Example of Manufacturing Polymer Electrolyte

After 167.59 gram (900 millimole) of 4,4′-dihydroxybiphenyl (DOD) and600 gram of benzophenone was heated, stirred and solved, 132.68 gram(960 millimole) of kalium carbonate and 180 milliliter of toluene wasadded there to, and heated to azeotropically hydrated. Then 200.52 gram(850 millimole) of m-dibromobenzene was added thereto at 180° C., 0.43gram (3 millimole) of copper bromide (I) was added in order, and stirredfor six hours while being kept at 200° C. Reaction solution was cooledand poured into a solution containing hydrochloric acid/methanol/acetonein the ratio of 2/70/30 in weight; precipitated polymers were filtered,washed with water, washed with methanol, and dried under reducedpressure to manufacture a polymer a1.

Then, 144 gram of SUMIKAEXCEL PES5003P (manufactured by SUMITOMOCHEMICAL, hydroxyl terminated polyether sulfone), 48 gram of the polymera1 was dissolved in DMAc, and 4.84 gram (35.0 millimole) of kaliumcarbonate and 9.52 gram (28.5 millimole) of decafluorobiphenyl was addedsequentially and stirred for four hours at 80° C. Reaction solution wascooled; a reaction mixture was poured into diluted hydrochloric acid toprecipitate a polymer. The precipitated polymer was washed with water,and washed with methanol to obtain a block copolymer a2. Then, the a2was sulfonated using concentrated sulfuric acid by an ordinary method toobtain a sulfonated bolock copolymer A shown below.

Ion exchange capacity of sulfonated block copolymer A was 1.4 meq/g.

It was confirmed by 1H-NMR measurement that the sulfonated blockcopolymer A has a structure in which only a1-derived moiety issulfonated to be a hydrophilic moiety and a PES5003P-derived moiety ishydrophobic moiety.

The sulfonated block copolymer A was used to be dissolved in DMAc toprepare polymer electrolyte solution of 25 wt %. The solution was castedon a glass plate and dried at 80° C. under normal pressure. The polymerelectrolyte film (1) thus obtained was measured with transmission typeelectron microscope and it was confirmed that the sum of value of thesize of hydrophobic domain and that of hydrophilic domain of a+b is 50nanometers.

Reference Example 2 Example of Manufacturing Polymer Electrolyte

(Synthesis of Polyether Sulfones (b1))

In a nitrogen atmosphere, 1500 gram of hydroxyl terminated polyethersulfone (SUMIKAEXCEL PES4003P manufactured by SUMITOMO CHEMICAL) wasdissolved in 4000 milliliter of DMAc. Further, 13 gram of kaliumcarbonate and 600 milliliter of toluene was added thereto, heated andhydrated under the azeotropic condition of toluene and water, and thetoluene was removed by distillation. Reaction solution was air-cooleddown to a room temperature; 123.2 gram (368.8 millimole) ofdecafluorobiphenyl was added thereto to carry out a reaction while beingheated gradually to 100° C. Then, the reaction solution was charged inmethanol to precipitate a polymer, the polymer was filtered and dried toobtain polyether sulfones (b1). The polyether sulfones (b1) werepolyether sulfone whose terminal group was substituted by anonafluorobiphenyloxy group.

(Synthesis of Block Copolymer B)

In a nitrogen atmosphere, 96.8 gram (0.424 mole) of hydroquinone kaliumsulfonate, 202.9 gram (0.414 mole) of 4,4′-difluorodiphenylsulfone-3,3′-kalium disulfonate and 61.6 gram (0.445 mole) ofkalium carbonate was dissolved in 2600 milliliter of DMSO. Then 500milliter of toluene was added thereto, heated and stirred, dehydratedunder the azeotropic condition of toluene and water, and the toluene wasremoved by distillation. Reaction solution was heated for seven hourswhile being stirred at 170° C., and air-cooled down to a roomtemperature to obtain a polymer (b2). Then 350 gram of the polyethersulfones (b1) was added thereto, and reacted while being cooled downgradually to 140° C. Then, the reaction solution was charged in methanolto precipitate a polymer; the polymer was filtered, washed twice withhot water of 95° C. in a volume of approximately five times based on thereaction solution, and dried to obtain a sulfonated block copolymer Bdescribed below.

A sulfonated block copolymer B has a molecular weight in terms of apolystyrene measured by GPC of Mn=72000, Mw=390000; and ion exchangecapacity of 1.43 meq/g. It was confirmed by 1H-NMR measurement that theblock copolymer B was a block copolymer having a structure in which onlya (b2)-derived moiety that is sulfonated is a hydrophilic moiety, and apolyether sulfones (b1)-derived moiety is hydrophobic moiety.

The sulfonated block copolymer B was used to be dissolved in NMPc toprepare polymer electrolyte solution of 25.5 wt %. The solution wascasted on a glass plate and dried at 80° C. under normal pressure. Thepolymer electrolyte film (2) thus obtained was measured withtransmission type electron microscope and it was confirmed that the sumof value of the size of hydrophobic domain and that of hydrophilicdomain of a+b is 19 nanometers.

Reference Example 3 Example of Manufacturing Polymer Electrolyte

A mixture of having a sulfonated block copolymer B obtained by referenceexample 2 and a polymer containing a phosphonic acid group that issynthesized as described below in the ratio of 90:10 in weight was usedto be dissolved in NMPc to prepare polymer electrolyte solution of 27 wt%, the solution was casted on a glass plate and dried at 80° C. undernormal pressure. The polymer electrolyte film (3) thus obtained wasmeasured with transmission type electron microscope and it was confirmedthat the sum of value of the size of hydrophobic domain and that ofhydrophilic domain of a+b is 19 nanometers.

(Synthesis of Polymer Containing a Phosphonic Acid Group as StabilizingAdditives)

According to a method disclosed by JP-A-H10-021943, in the presence ofdiphenylsulfone and kalium carbonate as a solvent, 4,4′-dihydroxydiphenylsulfone, 4,4′-dihydroxy biphenyl and 4,4′-dichlorodiphenylsulfone was reacted in the ratio of 7:3:10 in mole ratio toprepare a random copolymer shown below.

Then according to a method disclosed by JP-A-2003-282096, the copolymerwas brominated, phosphonic acid-esterified and hydrolyzed to obtain apolymer containing a phosphonic acid group shown below in whichapproximately 0.1 piece of Br and approximately 1.7 piece of phosphonicacid group was substituted per one unit of 4,4′-biphenol-derived unit.

Examples 1 to 3

A polyethylene-made porous film A was fixed at a glass plate, a polymerelectrolyte solution, prepared in the same way as that of referenceexamples 1 to 3, was dropped on the porous film. The polymer electrolytesolution was spread evenly over the porous film by using a wire coater,a coat thickness was controlled by using a bar coater having theclearance of 0.3 milimeter and dried at 80° C. under normal pressure.Then, it was dipped in 1 mol/L of hydrochloric acid, further was washedwith ion-exchange water to obtain a polymer electrolyte compositemembrane.

The fuel cell characteristic of the polymer electrolyte compositemembrane was evaluated and the result was shown in Table 1.

Comparative Example 1

A polymer electrolyte composite membrane was obtained according toExample 1 except that a polyethylene-made porous film B was used. Thefuel cell characteristic of the polymer electrolyte composite membranewas evaluated and the result was shown in Table 1. TABLE 1 Voltage E(V)0.8 0.6 0.4 0.2 Current value I (A/cm²) Example 1 0.08 0.40 0.98 1.28Example 2 0.20 0.89 1.40 1.70 Example 3 0.17 0.17 1.10 1.40 ComparativeExample 1 0.06 0.10 0.21 0.35

INDUSTRIAL APPLICABILITY

The present invention can provide a polymer electrolyte compositemembrane that exhibits high power generating performance by using aspecific polymer electrolyte having a phase-separated structure of ahydrophobic moiety and a hydrophilic moiety in a solid state, and thesum of the size of hydrophobic domain and that of hydrophilic domain inthe phase-separated structure is equal to or less than the average porediameter of fine pores of a porous base material.

Further, a polymer electrolyte composite membrane according to theinvention is advantageous as an electrolyte membrane not only for fuelcells using hydrogen as fuel but for fuel cells using alcohol such asdirect methanol type fuel cell because the polymer electrolyte compositemembrane exhibits high power generating performance.

1. A polymer electrolyte composite membrane comprising a porous basematerial having fine pores which is fill with a polymer electrolytecomprising a hydrophobic moiety and a hydrophilic moiety. wherein eachphase of the hydrophobic and a hydrophilic moieties of the polymerelectrolyte satisfy the following formula (1)a±b≦d  (1) (wherein a represents the size (nm) of a hydrophobic domain,b represents the size (nm) of a hydrophilic domain, and d represents theaverage pore diameter (nm) of fine pores of the porous base material).2. The polymer electrolyte composite membrane according to claim 1,wherein the formula (1) is a±b≦d/2.
 3. The polymer electrolyte compositemembrane according to claim 1, wherein a value of a+b is equal to ormore than 3 nanometers.
 4. The polymer electrolyte composite membraneaccording to claim 1, wherein a value of a±b is equal to or more than 10nanometers.
 5. The polymer electrolyte composite membrane according toclaim 1, wherein a value of a+b is equal to or less than 200 nanometers.6. The polymer electrolyte composite membrane according to claim 1,wherein a value of a+b is equal to or less than 100 nanometers.
 7. Thepolymer electrolyte composite membrane according to claim 6, wherein ahydrophilic repeating unit has an ion-exchange group.
 8. The polymerelectrolyte composite membrane according to claim 7, wherein anion-exchange group is cation-exchange group or anion-exchange group. 9.The polymer electrolyte composite membrane according to claim 8, whereina cation-exchange group is at least one selected from a group consistingof —SO₃H, —COOH, —PO(OH)₂, —POH(OH), —Ph(0H) (Ph represents a phenylgroup).
 10. The polymer electrolyte composite membrane according toclaim 9, wherein an anion-exchange group is at least one selected from agroup consisting of —NH₂, —NHR, —NRR′, —NRR′R″⁺—NH₃ ⁺ (R represents analkyl group, cycloalkyl group, aryl group, etc.).
 11. A polymerelectrolyte composite membrane having a continuous phase-separatedstructure in which a hydrophobic moiety and a hydrophilic moiety ofpolymer electrolyte are parallel to a membrane thickness direction. 12.Method for manufacturing a polymer electrolyte membrane by compositing aporous base material and a polymer electrolyte comprising a hydrophobicmoiety and a hydrophilic moiety, and each phase of the hydrophobic andthe hydrophilic moieties of the polymer electrolyte satisfy thefollowing formula (1)a±b≦d  (1) (wherein a represents the size (nanometer) of a hydrophobicdomain, b represents the size (nanometer) of a hydrophilic domain, and drepresents the average pore diameter (nanometer) of fine pores of theporous base material).
 13. The method for manufacturing a polymerelectrolyte membrane according to claim 12, wherein the methodcomprising of dissolving a polymer electrolyte in solvent, impregnatinga porous base material with the solution, taking out the porous basematerial, drying solvent, and then compositing the porous base materialand the polymer electrolyte.
 14. The method for manufacturing a polymerelectrolyte membrane according to claim 13, wherein the methodcomprising of dissolving a polymer electrolyte in solvent, applying thesolution on a porous base material, drying solvent, and then compositingthe porous base material and the polymer electrolyte.
 15. The method formanufacturing a polymer electrolyte membrane according to claim 13,wherein the method comprising of dissolving a polymer electrolyte insolvent, contacting a porous base material with the solution underreduced pressure, then returning the pressure to a normal pressure,drying solvent, and then compositing the porous base material and thepolymer electrolyte.
 16. A fuel cell comprising the polymer electrolytecomposite membrane according to claim 1.